April 5, 2012Paul Ducheney Superintendent – Hydro Holyoke Gas and Electric Department 99 Suffolk Street Holyoke, MA 01040-5082
The Connecticut River Watershed Council, Inc. (CRWC) agrees that the work proposed by HG&E as discussed on the March 8, 2012 conference call is aimed at meeting the Settlement goal for downstream shortnose sturgeon passage at the Project, and CRWC agrees that HG&E should move forward with design and permitting.
Some of the key elements of the design as agreed upon currently are summarized as follows:
- Installation of a new angled bar rack in front of the turbines, with 6-inch rack bars and a 2-inch clear space.
- Solid overlays will be placed on the rack over units 1 and 2 on the full width of the rack down to a bottom elevation of 95 ft.
- Solid overlays will be added on the horizontal section of the rack just upstream of the weir and on the adjacent sloping portion of the rack next to the dam, down to the third structural member (as shown in Figure 1 in the February 2010 narrative for new CFD runs 21 and 22. Note the committee decided this was preferable than Figure 2).
- A cut-off wall will be added between the weir and the Unit 1 intake to prevent fish from entering the low velocity eddy in that region.
- HG&E proposes to install a new turbine at Hadley Unit 1. The unit proposed has a radial clearance of 0.085 inches, thicker entrance edges for the runner blades, and a smoother operation during high flow, new wicket gates to provide smoother passage through stationary water passage components.
- A potential flow allocation plan under the inclined rack configuration was distributed to us dated March 2012.
- At the downstream end, plunge pool will be designed according to revision 3 as modeled in CFD model Run L dated June 2011.
The current design is the best attempt over the course of more than five years of studies, designs, modeling, and comments by HG&E, their consultants, and the CCT. The design has not been tested in the field, so we do not know for sure that sturgeon will find and use this passage route, and we also only have estimates of passage survival. As we have discussed in meetings, concerns related to lateral flow to the weir, flows across the depth of the water column, success in regard to getting sturgeon to swim to the surface in order to reach the weir, impingement and entrainment of eels, and fish reaction to the corner near the weir entrance will be addressed in the context of post-construction monitoring.
Andrea F. Donlon, M.S.